1. Field of the Invention
The invention relates to a hydrostatic drive with a hydraulic pump and a plurality of hydraulic motors that are hydraulically linked with said hydraulic pump as well as a method for operating such a hydrostatic drive.
2. Discussion of the Prior Art
A hydrostatic drive according to the present state of the technology is known from DE 35 43 073 C2. In the case of the hydrostatic drive described in this patent an adjustable hydraulic pump is driven by a combustion engine. In a functional circuit a plurality of hydraulic motors is arranged parallel to each other, which each drive different vehicle wheels. The hydraulic motors are likewise designed to be adjustable. One speed sensor which is linked with an electronic control device is allocated to each hydraulic motor or each vehicle wheel. The pivot angle of the hydraulic motors is set synchronously for all hydraulic motors.
If slipping occurs on one of the vehicle wheels owing to reduced surface grip the problem arises that this vehicle wheel spins and the speed of the allocated hydraulic motor increases considerably in comparison to the speed of the other hydraulic motors. As a result a considerable volume flow passes through that hydraulic motor, the vehicle wheel of which is subjected to slipping, as a result of which the volume flow available to the other hydraulic motors, via which the drive operates, is reduced. As a result the efficiency of the hydrostatic drive is substantially lower.
In order to prevent this, it is proposed in DE 35 43 073 C2 to continually compare the speeds of the individual vehicle wheels or hydraulic motors with each other in the electronic control device. If considerable deviation in the speed of one of the vehicle wheels in comparison to the speed of the other vehicle wheels occurs, then this indicates slipping on this vehicle wheel. The hydraulic pivot angle control of the vehicle wheel concerned is overridden by an electromagnetically-operated control valve so that the intake volume of the hydraulic motor allocated to the vehicle wheel concerned is reduced by pivoting back the hydraulic motor.
A disadvantage when that hydraulic motor, the vehicle wheel of which is subjected to slipping, pivots back as proposed in DE 35 43 073 C2 is however that as a result of the hydraulic motor pivoting back, although the volume flow passing through this hydraulic motor is reduced and therefore is available to the other hydraulic motors, at the same time acceleration of the associated vehicle wheel can be linked with the pivoting back of the hydraulic motor, while the pivot angle of the hydraulic pump and of the other hydraulic motors remains constant and therefore a further rise in the speed, particularly, if the rotation of the vehicle wheel is not subject to any friction related to surface grip. This measure therefore does not exclude the risk of the pivoted back hydraulic motor overspeeding.
From DE-AS 21 35 279 a hydrostatic drive with a variable hydraulic pump and a single variable hydraulic motor in combination with a vehicle brake is known as such. The vehicle brake can be pneumatically operated by means of a brake pedal. The pneumatic brake valve is linked with the hydraulic control device so that the hydrostatic gears change down when the vehicle brake is applied, in order to prevent a counter-force arising between the drive via the hydrostatic gears and the vehicle brake. In addition a speed sensor, which triggers the vehicle brake when the speed of the combustion engine reaches its permitted maximum, is arranged on the shaft of the combustion engine connecting with the hydraulic pump. As a result of braking the vehicle the maximum speed is prevented from being exceeded and therefore overspeeding of the combustion engine is avoided. This patent however gives no indication of using the vehicle brake in conjunction with anti-slip regulation on a hydrostatic drive.